Unit Operations

Major components of the BIOLAC® systems are the aeration equipment and the clarifier and solids handling equipment.

4.10.2.2.1 Aeration Chains and Diffuser Assemblies

The unique feature of BIOLAC® systems is the floating aeration chain system (Figure 4.2). Fine bubble diffusers are suspended from a floating aeration chain that carries air to the diffusers. The floating aeration chain is attached to an anchor on the embankment and is allowed to move in a controlled way to create the oxic and anoxic zones discussed above. Each diffuser assembly can support two, three, four, or five diffusers. Each diffuser is rated at 2 to 10 scfm and normally operates at an airflow rate of 6 scfm. Diffuser membranes are expected to last about 5 to 8 years before replacement is required.

4.10.2.2.2 Blowers and Air Manifold

Continuous-service positive displacement rotary blowers are generally used. In larger systems, multistage centrifugal blowers may be more economical. Most systems use three blowers, each capable of providing 50% of the required airflow and one unit serving as a spare.

4.10.2.2.3 Clarification and Solids Handling

An integral clarifier is used with the BIOLAC-R system, although conventional clarifiers are used on occasion. BIOLAC-L systems require installation of a polishing basin for solids separation and storage. A cross-sectional view of the integral clarifier is shown in Figure 4.22. The integral clarifier is constructed in the aeration basin but is separated from the aeration zone by a partition wall. Flow enters the clarifier along the bottom over the entire length of the partition wall to minimize short-circuiting. A flocculating rake moves the length of the clarifier sludge trough to concentrate and distribute the sludge. Sludge return and waste are removed with an air-lift pump.

Influent

Time: t = 0 minutes Return Activated Sludge

Anoxic

Oxic

Anoxic

Oxic

Oxic

Effluent

Anoxic

Effluent

Anoxic

Influent

Time: t = 15 minutes Return Activated Sludge

Oxic Anoxic

Oxic

Anoxic

Oxic

Effluent

FIGURE 4.21 Wave-Oxidation© modification of the BIOLAC-R system. (Courtesy of Parkson Corp., Ft. Lauderdale, FL.)

4.10.2.2.4 BIOLAC-L Settling Basin

A minimum hydraulic retention of one day is normally provided in the unaerated section of the polishing basin. Sludge storage of up to 1 to 2 decades is provided in the quiescent zone of the polishing or settling basin. Further sludge degradation of 40 to 60% occurs under anaerobic conditions in the settling basin.

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